The present invention relates to electronic power conversion circuits, and more specifically, to switching type power converter circuits.
Many systems employ power converter circuits. These circuits receive electrical power in one form and convert it to another form, for example, to a form that is usable by electrical equipment employed within the particular system.
One type of power converter circuit is referred to as a switching type power converter circuit or simply a switching power supply. Switching type power converter circuits make use of switches, as well as capacitors, inductors and/or transformers, in order to convert the electrical power from one form to another. These switches have an on state and an off state. The on state is sometimes referred to as the closed state or the conducting state. The off state is sometimes referred to as the open state or the non-conducting state.
As with many power converter circuits, a switching type power converter circuit is often expected to operate with a particular level of efficiency and to provide a particular level of regulation over line and load changes.
The efficiency of a switching type converter circuit depends in part on the amount of power that is dissipated across the switches. The power loss across the switches is equal to the product of the voltage across the switch and the current through the switch. In this regard, the losses during the transitions from the on state to the off state, and vice versa, are often the main design concern. (When the switch is in the on state, the voltage across the switch is ideally zero. When the switch is in the off state, the current through the switch is zero.) Losses can occur during the transition from the on state to the off state, and vice versa, if there is a non-zero voltage across the switch and non-zero current through the switch. Such losses are proportional to the product of the power lost per transition and the switching frequency. Therefore, to reduce the losses across a switch, a zero-current condition is desired while the switch transitions from the on state to the off state, and a zero-voltage condition is desired while the switch transitions from the off state to the on state.
Several techniques have been introduced, which accomplish zero-voltage switching inherently at constant switching frequency. One of these techniques requires a full-bridge switching arrangement with four primary switches in which the regulation is accomplished by shift phase modulation. This technique has several drawbacks including the limited availability of phase-modulated integrated control circuits and the large number of parts, which include four primary switches, at least two secondary switches and at least two large magnetic circuit elements. The technique suffers from an inability to accomplish zero-voltage switching at light loads without additional circuit elements and additional complexity.
Another circuit to address this purpose is based on the single-ended forward converter that accomplishes zero-voltage switching by addition of an extra primary side switch and capacitor. Disadvantages of this converter include in additional voltage stress on the primary switching elements required to reset the transformer core. The parts required are two large magnetic circuit elements, the transformer and the filter inductor, two primary switches, a large primary capacitor, and two secondary switching elements.
There is one example of prior art that accomplishes a zero-voltage switching converter, which has a single magnetic circuit element, accomplishing both magnetic energy storage and isolation. This converter relies on high AC magnetizing fields in order to accomplish zero-voltage switching, requiring that the magnetizing field and the magnetizing current change sign during each cycle. However, these increased losses impose a limit on the level of power density and efficiency that can be obtained with this approach.
Notwithstanding the performance level of current switching type power converter circuits, further improvements are sought.
According to one aspect of the present invention, a power converter apparatus is provided. The power converter apparatus comprises a step-down converter circuit of switching type having an input port to couple to a supply voltage and having an output port to provide an output voltage at a magnitude that is lower than a magnitude of the supply voltage, and having a control circuit to receive a feedback signal and regulate the magnitude of the output voltage in response thereto; a DC/AC converter circuit of switching type having a primary side and a secondary side, the primary side having an input port coupled to the output port of the step-down converter circuit, the secondary side having an output port to provide an AC output voltage; a rectifier circuit having an input port and an output port, the input port being coupled to the secondary side of the DC/AC converter circuit, the output port supplying a DC voltage; and a feedback circuit to generate the feedback signal in response to the output port of the rectifier circuit.
According to another aspect of the present invention, a power converter apparatus is provided. The power converter apparatus comprises step down converter means for receiving a supply voltage and generating an output voltage at a magnitude that is lower than a magnitude of the supply voltage, the step down converter means including means for regulating the output voltage in response to a feedback signal; a DC/AC converter circuit of switching type having a primary side and a secondary side, the primary side having an input port coupled to the output port of the step-down converter circuit, the secondary side having an output port to provide an AC output voltage; a rectifier circuit having an input port and an output port, the input port being coupled to the secondary side of the DC/AC converter circuit, the output port supplying a DC voltage; and a feedback circuit to generate the feedback signal in response to the output port of the rectifier circuit.
According to another aspect of the present invention, a power converter apparatus is provided. The power converter apparatus comprises a step down converter means for receiving a supply voltage and generating an output voltage at a magnitude that is lower than a magnitude of the supply voltage, the step down converter means including means for regulating the output voltage in response to a feedback signal; a DC/AC converter means for receiving the output voltage of the step down converter means and providing an AC output voltage; a rectifier means for coupling to the secondary side of the DC/AC converter means and supplying a DC voltage; and a feedback means for receiving the DC output voltage of the rectifier means and generating the feedback signal supplied to the step down converter means.
According to another aspect of the present invention, a method for a power converter is provided. The method comprises: receiving a supply voltage and generating a first output voltage having a magnitude that is lower than a magnitude of the supply voltage, where the act of generating comprises regulating the first output voltage in response to a feedback signal; generating an AC voltage from the first output voltage; rectifying the AC voltage to provide a DC voltage; and generating the feedback signal in response to the DC voltage.
Notwithstanding the potential advantages of one or more embodiments of one or more aspects of the present invention, it should be understood that there is no requirement that any embodiment of any aspect of the present invention address the shortcomings of the prior art.